I HAVE spent my professional life discovering how disease-causing bacteria resist antibiotic treatment. The public should understand that antibiotics can treat bacterial infections, but not viruses, and the full prescription must be taken. Everyone using antibiotics shares the responsibility for increased bacterial resistance, so they must also take a role in using these important resources responsibly.

Yet drug-resistant bacteria emerge not only because people take the drugs, but also from the drugs’ use in agriculture. Worldwide, the livestock industry consumes approximately twice the amount of antibiotics as are prescribed for humans.

In 2003, the World Health Organization found clear evidence of adverse human-health consequences due to resistant bacteria from nonhuman usage.

Scientists, including myself and my peers worldwide, worry that the current, widespread use of low-dose antibiotics in animal feed constitutes a human-health hazard.

Many antibiotics are given to healthy food animals such as cattle, pigs and chickens to promote growth, usually administered in food and water to the entire herd or flock. This practice employs smaller concentrations of antibiotics than is typically used to treat bacterial infections.

Low concentrations of antibiotics, whether in animals or people, kill the susceptible bacteria but select for bacteria that survive because of genetic changes. This leads to the selection of antibiotic-resistant and multidrug-resistant bacteria, also known as superbugs.

Antibiotics have been used for over 60 years, so many bacteria have developed resistance against multiple antibiotics, reducing treatment options. Most older, inexpensive antibiotics, such as penicillin and tetracycline, no longer effectively cure diseases in humans or animals. This results in the need for more expensive antibiotics. In extreme cases, no appropriate antibiotics currently exist.

Antibiotic use in food animals and the relationship to the development of resistant bacteria that affect humans has been the subject of a long, hostile and ongoing discussion in the U.S. Food and Drug Administration.

The FDA began to limit the use of penicillin and tetracycline in animal feed as growth promoters 35 years ago, but never completed the process because the U.S. House and Senate budget committees passed resolutions against the ban.

In 2001, the FDA recommended collection of data on antibiotic-resistant, food-borne pathogens and research to find the levels of resistance in pathogens that would significantly affect human health. Once the threshold was reached, FDA would stop or restrict use of that particular antibiotic. Bans exist for particular fluoroquinolones.

Last year, the FDA called for voluntary restrictions on the use of cephalosporins as growth promoters, but this drug can still be used to prevent disease. Voluntary guidelines alone won’t significantly change practice or use.

Europe banned antibiotics as growth promoters in 2006. In Denmark, antibiotic usage dropped 50 to 60 percent in livestock production. Denmark also prohibits veterinarians from profiting from the sale of antibiotics to farmers, which is a practice that continues in the United States. The Danes found no negative impact on production or feed quantities used. Since these measures were implemented, Denmark’s pork production has increased.

Diners and shoppers should be mindful of where their food comes from since many countries that export food to the U.S. use even more antibiotics than this country uses for production. Buying antibiotic-free meat does not necessarily protect people because while it does not contain antibiotic residue, it may still contain drug-resistant bacteria.

Cooks can protect diners by handling food properly and cooking meat to recommended temperatures. Eating unpasteurized dairy products or eggs are often linked to food-borne illnesses.

The U.S. Senate’s health committee missed an opportunity recently to include provisions that would improve annual reporting of antibiotic sales for use on industrial farms. Separate legislation is being introduced to address the matter and I hope our state’s congressional delegation will support it.

Dozens of other scientists, medical professionals and ordinary moms and dads were in Washington, D.C., Tuesday to educate Congress on the need for meaningful action on the livestock industry’s antibiotic use.

Bacteria may become more resistant every time they encounter an antibiotic. The question for the future is how to preserve the potency of existing antibiotics in the face of bacteria’s ability to become antibiotic resistant.

The success of Denmark’s farms can be reproduced on U.S. farms. It would result in lower use of antibiotics, without negatively impacting food production or costs.

Marilyn C. Roberts has a doctorate in microbiology and immunology and is a microbiologist at the University of Washington. The opinions are her own and do not reflect the UW.